1. Field of the Invention
The embodiments of the invention relate to a liquid crystal display device, and more particularly, to a light emitting diode (LED) backlight unit and a liquid crystal display device including the backlight unit.
2. Discussion of the Related Art
In general, a notebook personal computer (NTPC) includes a liquid crystal display (LCD) device for displaying information. An LCD device includes a liquid crystal display panel, a backlight unit and a driving circuit unit. The liquid crystal display panel includes a plurality of liquid crystal cells disposed in matrix and a plurality of thin film transistors (TFTs) through which image signals are supplied. Rotation angles of liquid crystal molecules in each liquid crystal cell as well as transmittance through each liquid crystal cell are controlled according to the image signals so as to display images on the liquid crystal display panel. The backlight unit is disposed under and supplies light to the liquid crystal panel. A cold cathode fluorescent lamp (CCFL) is used as a light source for the backlight unit of an LCD device. The backlight unit should be designed to have a thin profile and light weight but yet provide a large amount of light to the liquid crystal display panel. Light emitting diodes (LEDs) have been suggested for use in a backlight unit because LEDs have the characteristics of low power consumption, light weight and high brightness compared to a CCFL.
FIG. 1 is a view showing an edge type backlight unit according to the related art. In FIG. 1, an LED backlight unit includes an LED array 10 having a flexible printed circuit (FPC) 12 and a plurality of LEDs 11 on the FPC 12 and an LED driving unit 20. The LED driving unit 20 controls the plurality of LEDs 11 being turned ON/OFF using an LED driving source power and an LED control signal from an external circuit unit (not shown).
The LED backlight unit may be classified according to luminance and color rank of chromaticity coordinates for application to an LCD device. The luminance may be represented by luminance intensity or luminance flux, and chromaticity coordinates may be represented by CIE (Commission International De L'eclairage) 1931 (x-y coordinates) or CIE 1976 (u′-v′ coordinates). Ideally, the plurality of LEDs for a single LCD device should have the same luminance and the same color rank in chromaticity coordinates as one another.
In actuality, different LEDs, especially amongst different batches of LEDs, can have different luminances and different color rank in chromaticity coordinates from one another. Improper luminance and/or improper color rank of chromaticity coordinates in the backlight unit can cause improper color representation in the LCD device. Further, diversity in the average luminance and average color rank of chromaticity coordinates for different backlight units can cause a non-uniform color representations amongst the different LCD devices made with the different backlight units.